Interpretive Summary: Various aspects of biochar utilization are currently being investigated by scientists: agronomic benefits (plant, microbe, nematode), economics, carbon sequestration, pyrolysis system optimization, bioenergy production, and environmental remediation. Large-scale biochar application must meet specific local needs of producers impacted by the scale of operation, available biomass, soil type, and local climate. Challenges and potential risk of biochar application must be considered. For example, inherent heterogeneity of biochar (resulting from both feedstock heterogeneity and operational variables) can make it difficult for farmers to produce biochar of consistent quality. Recommendations will be given on localized biochar utilization practices for site-specific, case-by-case biochar use based on the purpose of biochar application (that should be appropriate for the soil type), locally availability feedstock, as well as socioeconomic situations.

Technical Abstract:
Char(coal), and a broader term black carbon (that includes soot) has long been recognized as a normal environmental (including soil) constituent resulting from fire and industrial activities. Biochar soil amendment has received global interests as a tool for carbon sequestration in conjunction with bioenergy production. In addition to the active research in both academic and federal sectors, biochar has received significant interests from policy makers and practitioners, partly because of easily understood concept and application. Most importantly, farmers can produce biochars themselves by slow pyrolysis of agricultural wastes on-farm. Despite its popularity and field trials already taking place around the globe, biochar can give mixed results for intended application, most importantly on the crop yield. This chapter will explore the benefits and potential risks of biochar soil amendment with a particular emphasis on the structural components of biochars. Selected characterization methods will be discussed, especially microscopic and spectroscopic techniques that are useful for understanding micro- to nm scale interactions and for addressing biochar aging, but have thus far been underutilized.